Ultrasonic scanning apparatus

ABSTRACT

A pulse-echo method of ultrasonic scanning to investigate the interior of a body involves contacting the body with an ultrasonic transducer at a fixed point having a first axis therethrough which is fixed relative to the body, projecting a pulsed ultrasonic beam through the fixed point along a second axis which is fixed relative to the transducer, and rotating the transducer about the first axis while progressively varying the angular inclination of the second axis to the first axis. The beam path then describes a spirally wrapped conical surface with its apex at the fixed point, which means that the transducer does not track across the body, but simply rolls on it at the fixed point, and this alleviates the transducer/body coupling problems which otherwise arise. Apparatus for this purposes comprises a support structure to define the first axis, a circular arcuate carriageway rotatable about this axis to produce the wrapping motion and to define by its centre of curvature the fixed point, a carriage extending transversely from the carriageway to define the second axis and movable along the carriageway to produce the progressive angular variation or spiral effect, and a transducer with its periphery at the fixed point, its beam path along the second axis, and rotatably mounted in the carriage to effect a rolling action on the body.

United States Patent [191 Hill et al.

[ ULTRASONIC SCANNING APPARATUS {76] Inventors: Christopher Rowland Hill, 29 The Warren, Surrey, Carshalton; Victor Ralph McCready, 87 Grove Rd, Surrey, Sutton, both of England [22] Filed: Apr. 4, 1972 [21] Appl. No.: 241,012

[30} Foreign Application Priority Data Nolte 181/.5 BE

Primary Examiner-Benjamin A. Borchelt Assistant Examiner.l. V. Doramus AttorneyCushman, Darby & Cushman 1 Aug. 14, 1973 5 7 ABSTRACT A pulse-echo method of ultrasonic scanning, to investigate the interior of a body involves contacting the body with an ultrasonic transducer at a fixed point having a first axis therethrough which is fixed relative to the body, projecting a pulsed ultrasonic beam through the fixed point along a second axis which is fixed relative to the transducer, and rotating the transducer about the first axis while progressively varying the angular inclination of the second axis to the first axis. The beam path then describes a spirally wrapped conical surface with its apex at the fixed point, which means that the transducer does not track across the body, but simply rolls on it at the fixed point, and this alleviates the transducer/body coupling problems which otherwise arise. Apparatus for this purposes comprises a support structure to define the first axis, a circular arcuate carriageway rotatable about this axis to produce the wrapping motion and to define by its centre of curvature the fixed point, a carriage extending transversely from the carriageway to define the second axis and movable along the carriagewayto produce the progressive angular variation or spiral effect, and a transducer with its periphery at the fixed point, its beam path along the second axis, and rotatably mounted in the carriage to effect a rolling action on the body.

10 Claims, 2 Drawing Figures ULTRASONIC SCANNING APPARATUS This invention concerns ultrasonic scanning apparatus and more particularly such apparatus suitable for medical diagnostic purposes. Apparatus for this more general kind is in fact already available in various forms of which two are commonly referred to as A-scan and B-scan.

Briefly, in A-scan apparatus an ultrasonic transducer assembly is located in a static position relative to a subject and, by use of pulse echo techniques, makes available data, normally by way of a cathode ray tube display, regarding tissue boundaries and other interfaces or reflecting surfaces along the axis of the beam transmitted from the transducer assembly. B-scan apparatus employs the same techniques but involves movement of the transducer assembly and a related movement in the visual display whereby an accumulated photographic or equivalent record can be produced to provide a twodirnensional picture for subsequent study.

It is also possible to employ ranging techniques whereby data is obtained from a predetermined point along the beam, and in a two-dimensional mode of operation, this leads to the possibility of scanning a predetermined plane or surface within a subject. However, no clinically practicable implementation of this last possibility has yet been reported. The reason for this would appear to be the difficulty in effecting a suitable scanning movement for the transducer assembly. This last difficulty arises more particularly from the fact that the transducer assembly must normally be maintained in direct contact, or indirect contact through a liquid coupling, with the subject in order to reduce the otherwise significant attenuation in passage of the beam therebetween. In fact it is for this reason that twodimensional techniques conventionally employ the simplest possible sectoral scanning movement and, even then, the quality of result is very dependent upon the skill of the operator. An associated difficulty is that use of a conventional Cartesian co-ordinate scanning arrangement will be slow due to the necessary reversal of direction of movement at the end of each line of scan.

An object of the present invention is to reduce these difficulties and, to this end, there is provided ultrasonic scanning apparatusof the more general kind in question, and also a mode of ultrasonic scanning, whereby a surface within a subject is investigated by moving an ultrasonic transducer assembly so that the associated beam path traces a spiral locus in said surface while passing through a spatially fixed point within or closely adjacent to said assembly.

In order to clarify the present invention, the same will now be more fully described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 diagrammatically illustrates one embodiment of the invention in a side elevation, and

FIG. 2 similarly illustrates part of the embodiment of FIG. 1 in another side elevation viewed perpendicularly to FIG. 1.

The illustrated embodiment comprises a scanning unit 1, an A-scan unit2, a range control unit 3, and a display/recorder unit 4. The scanning unit comprises a generally cylindrical housing 5 having a framework of upper and lower circular disc platforms 6 held together in longitudinally spaced co-axial disposition by three connecting columns 7 which are disposed between the peripheral regions of the platforms, parallel to the axis of the platforms, and at uniformly spaced circumferential locations. The housing 1 is completed by a cylindri cal casing 8 connected around the platforms 6 and extending below the lower platform to terminate in an open-ended part-conical portion 9 including a flexible diaphragm 10.

A subsidiary platform 11 is carried below the lower platform 6, co-axially therewith, by a shaft 12 rotatably borne relative to both the lower and subsidiary platfonns.

Two pairs of rods 13 depend from the subsidiary platform to carry at their lowennost ends one each of a pair of two circular arcuate carriageways 14 which extend generally transversely within the casing 8 in spaced side-by-side disposition. Also, it is to beunderstood that the carriageways are located symmetrically relative to the common axis of the platforms so that the medial radii of the carriageways are equally and oppositely spaced from, and parallel with, such axis.

The carriageways l4 carry two similar carriages 15a and 15b which depend between respective opposite end portions of the carriageway assembly. Each carriage is supported by a plurality of rollers 16 extending laterally from both sides thereof to engage the upper and lower curved peripheries of both carriageways to trackthe carriages thereon. Also, the carriages are seen to be of bifurcated form having similar pairs of side members 17a, 17a and 17b, 17b connected by respective cross-members 18a and 18b therebetween.

- However, the carriages are not identical. The side members 17a of one carriage 15a are longer than the side members 17b of carriage 15b and turn towards the latter at their lower ends in generally L-shaping. These lower ends have a cross member 18a therebetween on which is mounted a bearing 19 having an ultrasonic transducer assembly 20 rotatably mounted therein. The carriage l7b, on the other hand, has a cross member 18b between the lower ends of its side members 15b,

which cross member carries a counterweight 21b extending towards the carriage 15a. The side members 17a also carry a counterweight 21a. The counterweights 21g and 21b are chosen in magnitude andposition so that the carriage assemblies are dynamically similar for the purposes of the operation discussed hereinafter.

At their upper ends the carriages 15a and 15b are provided with similar circular arcuate toothed racks 22a and 22b which each extend'fromthe associated carriage towards the other, above and in parallel relation with the carriageways; However, the racks are mutually off-set in the lateral direction.

The racks 22a and 22b are drivably connected with a differential unit 23 depending below the subsidiary platform 11. This unit 23 comprises a casing 24 fixed with the platform 11 from which it extends around the shaft 12 and between the racks 22a and 22b. The shaft 12 is formed with a helical worm gear 25 towards its lower end and meshes with two opposed helical gear wheels 26a and 26b journalled in the differential casing 24 for rotation about respective longitudinal axes which extend in parallel manner laterally across the racks 22a and 22b. Two pinions 27a and 27b are respectively fixed with the helical gear wheels 26a and 26b, and extend in mutually opposite directions therefrom along the helical gear axes to mesh with respective ones of the racks 22a and 22b.

A main gear wheel 28 is fixed above the subsidiary platform 11 in co-axial manner with the shaft 12, and meshes at its periphery with a drive gear wheel 29 fixed on the shaft 30 of an electric motor 31. The motor 31 is mounted above the lower platform 6 and its shaft 30 projects through this platform to drive the main gear wheel 28.

It has been noted earlier that the shaft 12 is rotatably borne relative to both the lower platform 6 and the subsidiary platform 11. In the former case the shaft 12 is journalled in and projects above a bearing 32 fixed on the lower platform 6, and in the latter in a bearing 33 fixed on the subsidiary platform 1 l. The bearing 33 and the upper end of the shaft 12 carry respective fixed gear wheels 34 and 35 which respectively mesh with gear wheels 36 and 37 forming part of a transmission control assembly. Apart from the gear wheels 34 and 35, this assembly is mounted on supports 38 extending from a bar 39 fixed between the upper and lower platforms 6, and the assembly comprises a sequence of a first rotary shaft 40, a first clutch 41, a second rotary shaft 42, a second clutch 43, and a fixed shaft 44. The first rotary shaft 40 depends through the lower platform 6 to carry the gear wheel 36, the first clutch 41 engages to couple the first and second rotary shafts 40 and 42, and the second clutch 43 engages to couple the second rotary shaft 42 with the fixed shaft 44. The two clutches are conveniently electrically operated and will normally be operated in opposition so that when either one is engaged the other is disengaged.

Considering the operation of the illustrated embodiment: when the first clutch 41 is disengaged and the second clutch 43 is engaged, the first point to note is that the latter engagement couples the fixed shaft 44 with the shaft 42, gear wheel 37, gear wheel 35, and the shaft 12 with its helical worm gear 25 to render these components non-rotatable; while shaft 40, gear wheel 36, gear wheel 34, the bearing 33, and the subsidiary platform 11 with other components connected therewith are free to rotate. Accordingly energisation of the motor 31 rotates its drive shaft 30 and gear wheel 29, the main gear wheel 28, and the subsidiary platform 11, differential unit casing 24, carriageways l4, and carriages a, 15b therewith around the longitudinal axis 45 of the central shaft 12. Since the central shaft 12 is held fixed while the helical gear wheels 26a, 26b rotate therearound with the differential unit casing 24, these wheels and their pinions 27a, 27b will rotate also about their respective axes. As a result, in this situation, the racks 22a, 22b are driven by their pinions to track their carriages 15a, 15b across the carriageways 14 in mutually opposite directions dependent on the direction of rotation of the motor 31. The helical gear wheels, pinions and racks are of like form so that the carriages are moved at equal rates, the pinions and racks are coupled so that the carriages are maintained at symmetrically opposed positions relative to the longitudinal axis 45 of the shaft 12, and the mutually facing peripheries of the carriage side members 17a, 1712 are radially directed" relative to the carriageways so that these 'peripherie's meet along the axis 45 in one limit of carriage movement. Also the transducer assembly 20 is'posi'tioned so that the path 46 of its ultrasonic beam is' radially directed in the same way as the inner periphery of the associated carriage side member 17a, while passing through a point 0 of the free end of the member which is substantially located at the centre of curvature of the carriageways, so that the beam path 46 describes a generally spirally wrapped conical" surface having a fixed apex at the point 0.

Ideally, the point 0 is coincident with the outer periphery of the transducer assembly whereby this assembly can be located in contact with a subject and effect the above scanning action by rolling around the point 0. The transducer assembly is mounted in rotary bearing 20 and connected with flexible diaphragm 10 to accommodate this action. In practice this ideal action may not always be possible, but it will be appreciated that only a very small relative movement occurs between the point of engagement of the transducer assembly and the subjectif the point 0 is closely adjacent the point of engagement, so that satisfactory coupling of the transducer assembly with the subject is possible.

The above scanning action can be readily defined by a polar co-ordinate system with the position of the carriages along the carriageway assembly relative to the axis 45 representing the radial component R, and the position of rotation about the axis 45 representing the angular component 0. Moreover, electrical signals representing these co-ordinate components can be derived from transducers, such as rotary potentiometers, coupled to appropriate parts of the apparatus, and such signals can be applied to control the scanning action of a cathode ray tube 47 in the display unit 4 in synchronism with that of the scanning unit. Also, it is to be noted that, since cathode ray tubes are normally scanned under Cartesian co-ordinate (x, y) control, such control signals are readily available in the forms (R sin0, R c050).

In any event, a first rotary potentiometer 48 is shown coupled between the gear wheels 34 and 35 to be driven by the former wheel during scanning. This potentiometer can be of linear form to provide a signal representing the arcuate distance S of the carriages along the carriageway from the axis 45, or of non-linear form to provide a signal directly representing the radial component R. In the former case the signal S can be used to represent R, but then introduces a distortion between the scanned and displayed spirally scanned courses with the latter progressively radially expanded towards its outer periphery compared to the former. However, while such distortion is not critical in practical application of the invention, it can be compensated electronically on the basis of the relatively simple geometrical relationship between S and R in the relevant scanning action.

A second rotary potentiometer 49 is shown drivably coupled to the gear wheel 34. This potentiometer conveniently provides signals representing sinO and cost), and it can also provide a signal representing 0.

Another factor to take into account is that the timegating effected by the range control unit is most easily carried out on a constant basis so that the displayed data relates to a surface at a constant distance from the point 0, that is to say a part-spherical surface. However, it is equally possible to progressively control the time-gating so that the displayed data relates to a planar surface radial to the axis 45. In this last case, the necessary progressive control is again a relatively straightforward matter based on the geometrical relationship between the arcuate length S, the angle 4) which the beam makes with the axis 45, and the desired depth of scanning plane along the axis 45 from the point 0.

In both cases, whether a surface or plane is scanned, the whole of the transducer signal can be applied to a computing facility, possibly by way of a tape or similar record of the signal, to provide data relating to a sequence of parallel surfaces or planes within the focal depth of the transducer assembly.

A further factor to note is that the speed of scanning across the relevant surface or plane by the ultrasonic beam will be greater as the carriages are further along the carriageway from the axis 45, assuming that the motor drive is constant. It will in fact, be normally desirable that the pulse-echo operation be carried out to provide uniformly spaced data along the spiral scanning path, and this can be obtained by controlling the pulse-echo operation in progressive varying manner in response to the radial component R, or the component S as an approximation thereto. Alternatively, of course, the speed of the motor drive can be progressively controlled in this way, but the former of the alternatives will normally be preferred. A related factor is that of pulse-echo frequency, and this will normally be as high as possible from a practical point of view to attain the highest possible resolution in the scanned data. In practice, this will normally be determined by the minimum period required to avoid error arising from continuation of echos from one pulse before another pulse is generated. For clarification, it is noted that a prototype of the illustrated apparatus requires a minimum delay of 1 ms between generation of successive pulses, and this is in an operation affording 1 mm spacing along a spirally scanned path at 5 cm depth from the point 0.

One remaining factor for consideration is that of terminating the action of the scanning unit 1 when the carriages reach the limits of the carriageway. These limits are denoted by limit switches 50 coupled with the potentiometer 48, and these switches serve to automatically free the carriages from further tracked movement along the carriage when a limit is reached. This is effected by actuation of a limit switch to reverse the states of the clutches 41 and 43, so that clutch 43 disengages the second rotary shaft 42 from the fixed shaft 44, while clutch 41 engages to drivably couple the shaft 42 with the first rotary shaft 40. The ratios between gear wheels 34 and 36, and 35 and 37, are chosen to be the same so that, with the clutch states reversed, the central shaft 12 is rotated synchronously with the differential unit 23. As a result the helical worm gear 25 rotates with the helical gear wheels 26a, 26b and so the pinions 27a, 27b are not driven.

The same synchronous rotation occurs for the potentiometer 48 so that the radial component representation becomes fixed. However, the potentiometer 49 is still driven to conform to the still changing angular component of the scanning unit disposition.

While the present invention has been more particularly described with reference to the illustrated embodiments, it will be appreciated that other embodiments are equally practicable within the broader expressions of the invention in the appendant claims. Similarly, the mode of scanning of the invention may be applicable in situations other than medical diagnosis but where similar difficulty arises in coupling for ultrasonic investigation of the interior of a body. Accordingly, the appendant claims take account of both method and apparatus aspects of the invention.

We claim:

l. A method of investigating the interior of a body which comprises:

bringing an ultrasonic transducer into engagement with said body at one point thereon to project an ultrasonic beam into said body along a first axis which is fixed relative to said transducer and passes through said point;

rotating said transducer about a second axis which is fixed relative to said body and passes through said point, and at the same time progressively changing the angular relationship between said first and second axes, whereby said first axis describes a spirally wrapped conical surface about said second axis, which surface has said point as its apex;

energising said transducer in pulsed manner;

detecting with said transducer echo signals arising from within said body in response to said pulsed energisation;

and displaying or recording selected components of said echo signals to represent data relating to a predetermined surface within said body.

2. Ultrasonic scanning apparatus for investigating the interior of a body, comprising:

a support structure having a first axis fixed relative thereto and passing longitudinally therethrough; an elongate carriageway rotatably supported by said structure for rotation about said first axis, and extending transversely from said first axis;

a first carriage depending from and carried by said carriageway for movement therealong;

a rotary bearing connected with said first carriage for rotation about a second axis which is fixed relative to said first carriage and intersects said first axis in a predetermined point;

first transmission means to rotate said carriageway about said first axis;

second transmission means to move said first carriage along said carriageway and, at the same time, to progressively vary the angular inclination of said first carriage to maintain intersection of said first and second axes at said point;

an ultrasonic transducer journalled in said rotary bearing with the periphery of said transducer passing through said point, to generate and project an ultrasonic beam along said second axis, and to detect echo signals resulting from reflection of said beam from within said body;

and positional transducer means coupled with said first and second transmission means to provide coordinate signals representing the position of said first carriage relative to said first axis.

3. Apparatus according to claim 2 wherein:

said carriageway is of circular arcuate form having said first and secnd axes radially directed relative thereto, and said point as centre of curvature;

and said first carriage is tracked with said carriageway to effect said progressive variation of angular inclination between said axes.

4. Apparatus according to claim 3 wherein said second transmission means comprises:

a first gear member;

securing means to hold said first gear member against movement relative to said support structure;

a second gear member connected with said carriageway for rotation therewith, and drivably coupled with said first gear member; and a third gear member connected with said first carriage for movement therewith, and drivably coupled with said second gear member.

5. Apparatus according to claim 4 wherein:

said first gear member is rotatably mounted relative to said support structure and said carriageway;

said securing means comprises a clutch assembly connected between said first gear member and said support structure, and between said first gear member and said first transmission means, and which assembly is operable to alternatively connect said first gear member with said support structure, and to drivably couple said first gear member with said first transmission means;

and said positional transducer means comprises a first positional transducer drivably coupled with said first transmission means to provide a signal representing the angular position of said first carriage about said first axis, and a second positional transducer drivably coupled between said first transmission means and said first gear member to provide a signal representing the radial position of said first carriage relative to said first axis;

and comprising limit switch means operable to provide signals representing predetermined positions for said first carriage along said carriageway and to cause operation of said clutch assembly.

6. Apparatus according to claim 5 wherein said first and second position transducers are of rotary form.

ond carriage depending from and carried by said carriageway for movement therealong, and coupled with said second transmission means in like manner to said first carriage for equal and opposite movement along said carriageway to balance said first carriage.

10. Apparatus according to claim 2 comprising:

means for energising said ultrasonic transducer to generate said beam in pulsed manner;

means for selecting components of said echo signals to represent data concerning a predetermined surface within said body;

and means responsive to said co-ordinate signals and said selected echo signal components to display or record said data. 

1. A method of investigating the interior of a body which comprises: bringing an ultrasonic transducer into engagement with said body at one point thereon to project an ultrasonic beam into said body along a first axis which is fixed relative to said transducer and passes through said point; rotating said transducer about a second axis which is fixed relative to said body and passes through said point, and at the same time progressively changing the angular relationship between said first and second axes, whereby said first axis describes a spirally wrapped conical surface about said second axis, which surface has said point as its apex; energising said transducer in pulsed manner; detecting with said transducer echo signals arising from within said body in response to said pulsed energisation; and displaying or recording selected components of said echo signals to represent data relating to a predetermined surface within said body.
 2. Ultrasonic scanning apparatus for investigating the interior of a body, comprising: a support structure having a first axis fixed relative thereto and passing longitudinally therethrough; an elongate carriageway rotatably supported by said structure for rotation about said first axis, and extending transversely from said first axis; a first carriage depending from and carried by said carriageway for movement therealong; a rotary bearing connected with said first carriage for rotation about a second axis which is fixed relative to said first carriage and intersects said first axis in a predetermined point; first transmission means to rotate said carriageway about said first axis; second transmission means to move said first carriage along said carriageway and, at the same time, to progressively vary the angular inclination of said first carriage to maintain intersection of said first and second axes at said point; an ultrasonic transducer journalled in said rotary bearing with the periphery of said transducer passing through said point, to generate and project an ultrasonic beam along said second axis, and to detect echo signals resulting from reflection of said beam from within said body; and positional transducer means coupled with said first and second transmission means to provide co-ordinate signals representing the position of said first carriage relative to said first axis.
 3. Apparatus according to claim 2 wherein: said carriageway is of circular arcuate form having said first and secnd axes radially directed relative thereto, and said point as centre of curvature; and said first carriage is tracked with said carriageway to effect said progressive variation of angular inclination between said axes.
 4. Apparatus according to claim 3 wherein said second transmission means comprises: a first gear member; securing means to hold said first gear member against movement relative to said support structure; a second gear member connected with said carriageway for rotation therewith, and drivably coupled with said first gear member; and a third gear member connected with said first carriage for movement therewith, and drivably coupled with said second gear member.
 5. Apparatus according to claim 4 wherein: said first gear member is rotatably mounted relative to said support structure and said carriageway; said securing means comprises a clutch assembly connected between said first gear member and said support structure, and between said first gear member and said first transmission means, and which assembly is operable to alternatively connect said first gear member with said support structure, and to drivably couple said first gear member with said first transmission means; and said positional transducer means comprises a first positional transducer drivably coupled with said first transmission means to provide a signal representing the angular position of said first carriage about said first axis, and a second positional transducer drivably coupled between said first transmission means and said first gear member to provide a signal representing the radial position of said first carriage relative to said first axis; and comprising limit switch means operable to provide signals representing predetermined positions for said first carriage along said carriageway and to cause operation of said clutch assembly.
 6. Apparatus according to claim 5 wherein said first and second position transducers are of rotary form.
 7. Apparatus according to claim 4 wherein: said first gear member comprises a helical worm gear and said second gear member comprises a helical gear wheel.
 8. Apparatus according to claim 4 wherein: said second gear member comprises a pinion wheel; and said third gear member comprises a circular arcuate rack connected with said first carriage in parallel and concentric disposition with said carriageway.
 9. Apparatus according to claim 2 comprising a second carriage depending from and carried by said carriageway for movement therealong, and coupled with said second transmission means in like manner to said first carriage for equal and opposite movement along said carriageway to balance said first carriage.
 10. Apparatus according to claim 2 comprising: means for energising said ultrasonic transducer to generate said beam in pulsed manner; means for selecting components of said echo signals to represent data concerning a predetermined surface within said body; and means responsive to said co-ordinate signals and said selected echo signal components to display or record said data. 